Washers for locking, e.g., for bolt securing purposes, having a plate-like shape and on preferably one side a pattern of radially extending teeth and on the other side a pattern of preferably radially extending cams and comprising a central hole for a bolt, a screw or the like fastening element, are previously known. A pair of washers are intended to be applied together, the cam patterns facing each other and tooth patterns being intended to engage a bolt head, a nut or the like and a support or the like, respectively.
In order to obtain an efficient engagement and to resist the considerable force applied to the fastening arrangement the washers are made of a hardenable steel and hardened.
Furthermore, in order to, among other things, resist corrosion, the washers are provided with a coating of zinc, which is applied electrolytically.
A serious problem related to this prior art technique is that during the electrolytic application of the zinc coating, hydrogen is developed, the hydrogen on an atomic scale being solved in the washer steel and causing so-called hydrogen embrittleness, the embrittlement being due to the fact that the hydrogen atoms solved locks dislocations in the steel and, thus, reduces the steel ductility.
To substantially reduce or totally eliminate the hydrogen embrittleness, the washers, which have been hardened and, normally, slightly tempered, are heat treated at about 200° C. for about 48 hours to drive the solved hydrogen out of the steel. This is of course an expensive and time consuming operation which, however, is necessary. Further, said heat treatment tends to add tempering to the hardened steel so that the intended hardness will not be maintained but considerably decreased.
Furthermore, today there is a need for harder washers to be combined with harder bolts and pin bolts for gripping by the washer pattern of teeth. However, such harder washers are obtained by increasing the carbon content to the steel which makes the washers even more sensitive to hydrogen embrittlement and additional tempering during said heat treatment.
One object of the present invention is to provide a method and a washer which offers a solution to the problems described above.